The present invention relates to an air bag device having an inflatable bag for restraining an occupant of a motor vehicle in the event of a collision of the vehicle and, more particularly, to an air bag device of the type having a bag which is inflatable by gas generated by the combustion of a gas generating agent.
An air bag device is one of various implementations extensively used to restrain an occupant of a motor vehicle in his or her seated position when the vehicle encounters a collision. The air bag device includes an inflatable bag which is mounted in a folded position on a steering wheel or similar member which is located in front of an occupant. When the device senses a collision, it feeds a jet of gas into the bag so that the bag is rapidly inflated toward the occupant who is thrown forward to thereby restrain the occupant.
Systems for inflating the bag available in the art may generally be classified into two types, i.e., a non-combustion type system which releases compressed gas instantaneously to introduce it in the bag, and a combustion-type system which burns an explosive or similar gas generating agent to introduce the resulting gas in the bag. In general, the combustion type system is predominant over the non-combustion type system because it is more compact in construction and therefore more advantageously mounted on a motor vehicle than the latter.
An air bag device using the combustion scheme mentioned above may be implemented by a gas generator in the form of a container which stores a gas generating agent therein, as disclosed in U.S. Pat. No. 4,183,550 by way of example. The container is mounted in an inflatable bag to protrude into the latter. When the gas generating agent in the container is burned, the resulting gas is caused to jet into the bag. A drawback with the gas generator in the form of a container is that it has to be made of metal or similar material which is rigid enough to withstand the high pressure of combustion gas, increasing the weight of the gas generator. When an air bag device having such a heavy gas generator is mounted on a steering wheel, it is apt to cause the steering wheel to vibrate during idling or similar operating condition and, therefore, it is necessary to provide a steering column and its associated members with an extra measure against vibrations.
Further, the gas generator protruding into the bag as mentioned above prevents the bag from being folded flat. Hence, the prior art air bag device of the kind described has substantial overall dimensions even when the bag is folded up. The protruding gas generator of course makes it impossible to provide the whole device with a shape which is free to choose. It follows that a location available for mounting the air bag device without impairing the appearance is extremely limited. In addition, since the container type gas generator is provided with only a fixed gas jetting position, it is not practicable to control the sequence of development of the bag.